International Journal of Modern Physics A

Integration by parts is used to reduce scalar Feynman integrals to master integrals.

We discuss an alternative to the Higgs mechanism which leads to gauge invariant masses for the electroweak bosons. The key idea is to reformulate the gauge invariance principle which, instead of being applied as usual at the level of the action, is applied at the level of the quantum fields. In other words, we define gauge invariant quantum fields which are used to build the action. In that framework, the Higgs field is not necessarily a physical degree of freedom but can merely be a dressing field that does not propagate. If the Higgs boson is not propagating, the weak interactions must become strongly coupled below 1 TeV and have a nontrivial fixed point and would thus be renormalizable at the nonperturbative level. On the other hand, if a gauge invariant Higgs boson is introduced in the model, its couplings to the fermions and the electroweak bosons can be quite different from those expected in the Standard Model.

We explore some aspects of the phenomenology of the Higgs sector in a model that includes right-handed neutrinos, with a mass of the order of the electroweak scale. In this model all scales arise from spontaneous symmetry breaking, thus the Higgs sector includes an extra Higgs singlet, in addition to the Standard Model Higgs doublet. The scalar spectrum includes two neutral CP-even states (h and H, with m_h < m_H) and a neutral CP-odd state (σ) that can be identified as a pseudo-Majoron. The parameter of the Higgs potential are constrained using a perturbativity criteria, which amounts to solve the corresponding RGE. The relevant Higgs branching ratios and some cross-sections are discussed, with special emphasis on the detection of the invisible Higgs signal at the LHC.

The thermofield dynamics, a real-time formalism for finite temperature quantum field theory, is used to calculate the rates for e⁺e^- reactions at finite temperature. The results show the role of temperature in defining a hadronic state after the plasma has been cooled down.

In the framework of factorization, based on the first-order of isospin violation, we study direct CP violation in the decay of including the effect of ρ–ω mixing. The CP violation depends strongly on Cabibbo–Kobayashi–Maskawa (CKM) matrix elements and the effective parameter, N_c. Recently, the experimental data for the branching ratios of are accurate and we can give the strong constraint on the range of N_c. We find that the CP violating asymmetry is large and ranges from -82% to -98% via ρ–ω mixing mechanism when the invariant mass of the π⁺π^- pair is in the vicinity of the ω resonance. We also discuss the possibility to observe the predicted CP violating asymmetries at the LHC.

In this work, we investigate a very important but unstressed result in the work of C. M. Bender, J.-H. Chen, and K. A. Milton, J. Phys. A39, 1657 (2006). These authors have calculated the vacuum energy of the iϕ³ scalar field theory and its Hermitian equivalent theory up to g⁴ order of calculations. While all the Feynman diagrams of the iϕ³ theory are finite in 0+1 space–time dimensions, some of the corresponding Feynman diagrams in the equivalent Hermitian theory are divergent. In this work, we show that the divergences in the Hermitian theory originate from superrenormalizable, renormalizable and nonrenormalizable terms in the interaction Hamiltonian even though the calculations are carried out in the 0+1 space–time dimensions. Relying on this interesting result, we raise a question: Is the superficial degree of divergence of a theory is representation dependent? To answer this question, we introduce and study a class of non-Hermitian quantum field theories characterized by a field derivative interaction Hamiltonian. We showed that the class is physically acceptable by finding the corresponding class of metric operators in a closed form. We realized that the obtained equivalent Hermitian and the introduced non-Hermitian representations have coupling constants of different mass dimensions which may be considered as a clue for the possibility of considering nonrenormalizability of a field theory as a nongenuine problem. Besides, the metric operator is supposed to disappear from path integral calculations which means that physical amplitudes can be fully obtained in the simpler non-Hermitian representation.

We present analytic solutions for membrane metric function based on transverse k-center instanton geometries. The membrane metric functions depend on more than two transverse coordinates and the solutions provide realizations of fully localized type IIA D2/D6 and NS5/D6 brane intersections. All solutions have partial preserved supersymmetries.

We consider a nonsingular origin for the universe starting from an Einstein static universe, the so-called "emergent universe" scenario, in the framework of a theory which uses two volume elements and Φd⁴x, where Φ is a metric independent density, used as an additional measure of integration. Also curvature, curvature square terms and for scale invariance a dilaton field ϕ are considered in the action. The first-order formalism is applied. The integration of the equations of motion associated with the new measure gives rise to the spontaneous symmetry breaking of scale invariance. After spontaneous symmetry breaking of scale invariance it is found that a nontrivial potential for the dilaton is generated. In the Einstein frame we also add a cosmological term that parametrizes the zero point fluctuations. The resulting effective potential for the dilaton contains two flat regions, for ϕ → ∞ relevant for the nonsingular origin of the universe, followed by an inflationary phase and ϕ → - ∞, describing our present universe. The dynamics of the scalar field becomes nonlinear and these nonlinearities are instrumental in the stability of some of the emergent universe solutions, which exists for a parameter range of values of the vacuum energy in ϕ → - ∞, which must be positive but not very big, avoiding the extreme fine tuning required to keep the vacuum energy density of the present universe small. Zero vacuum energy density for the present universe defines the threshold for the creation of the universe.